https://blog.jeremiahgrossman.com/2006/11/browser-port-scann...
Most (non-technical) Web users also don't run their own web servers, so they aren't affected. Among technical users, the proportion with NoScript is probably not as small.
Given the long and gory history of companies releasing insecure by default devices methods like this are a legitimate entry point into a network.
I mostly use the web for reading blogs and articles, so the loss of dynamic sites isn't troublesome, but it's certainly not for most users.
(Edit: Some numerical context I have enabled Javascript for 194 sites over the last five years, whereas I encounter several new sites daily.)
Yes.
Joking aside, I will add that I've been a NoScript/FlashBlock user for quite some time (more than a decade? I honestly can't remember), and while I run into some things that are frustrating (just had to disable NoScript for a tab to order plane tickets), it is refreshingly uncommon.
Yes, you can browse with default deny to JS and Flash.